This application relates in general to a method, apparatus, and article of manufacture for providing high speed digital communications through a backplane communications channel, and more particularly to a method, apparatus, and article of manufacture for providing a transceiver for, and system and method implementing a transceiver in a high speed digital signaling across a communications channel, for example, a backplane.
In conventional systems, communications across the backplane was accomplished using a Serializer-Deserializer (“SERDES”) and binary coding. While SERDES based systems employing binary coding are relatively straightforward to implement because of its simplicity, such systems may have a bandwidth limitation, which make them more difficult to implement as the density of bits per trace increase.
In order to meet the increase in the demand of the transfer rate of data, conventional systems also employ a multi-level pulse amplitude modulation (PAM-n) scheme that encodes a plurality of bits of data into or onto a signal in which the symbols are represented as a set of signal levels between a minimum and maximum set of signal levels. One advantage of utilizing multi-level PAM, as opposed to binary, is that fewer symbols per second need to be transmitted to convey a given number of bits per second. This reduces the frequency content of the transmitted signal.
A shortcoming of employing multi-level PAM signaling is a reduction in voltage margin. The reduction in voltage margin creates, among other things, the recovery or detection of the original signal more difficult and therefore recovery of the original symbol(s) more difficult. For example, detecting the level of a PAM-4 signaling technique requires discrimination between four levels rather than two levels in a binary signaling technique.
Moreover, while PAM-4 signaling allows for a two-fold reduction in the symbol rate for a given channel bit rate (relative to binary), systems employing PAM-4 tend to observe or experience a two-thirds smaller eye opening in terms of the voltage, and up to a two times larger eye opening in terms of the time domain relative to conventional binary signaling systems carrying the same aggregate bit rate. As such, nearly exact or precise equalization to a zero intersymbol interference pulse shape may be required to eliminate errors.
Thus, there is a need for a communications system for a backplane that addresses the higher density of bits per trace environments.